Sergeant Brenda Nichols had already worked 14 hours, investigated the death of one baby, juggled three priority cases, and reviewed dozens of others. She had been home a half hour when her phone rang again with an urgent message about another child.

Nichols grabbed her black police jacket and returned to the cold night. She steered her department-issued Chevy Impala back to Interstate 35 and headed north to Dallas.

On nights like these, the head of the Dallas Police Department’s Child Abuse Squad felt the crushing weight of her job. The stories of cruelty and violence never stopped. Friends worried that the work had become too much. How many dead children could one woman take?

From the quiet interior of her car, the lighted skyline of Dallas came into view. On the 11th floor of Children’s Medical Center, another baby was dying. A boy, 11 months old, wrapped in a blanket printed with dragonflies.

A small troupe of detectives, doctors, nurses, and caseworkers was assembling. Nichols steeled herself for the work that lay ahead, reminding herself, as she had so many times before, You wanted this job.

•••

Before going to the hospital, Nichols needed to make a stop. She pulled up to an old Victorian house on Swiss Avenue, the headquarters of the Child Abuse Squad for 20 years. Nichols, 51, supervised a unit of 11 detectives who investigated the sexual and physical abuse of children within the 385-square-mile city limits. They handled cases of abuse committed by caretakers, people who knew the children. Thousands of reports came in by phone, email, and fax every year. On some days, the reports were so severe and so abundant that Nichols and her team worked while the sun rose, set, and rose again. So it would be on this day, December 7, 2011.

It was just after 9 pm when Nichols walked through the darkened hallways toward a narrow corridor of gray cubicles on the second floor. The squad room was a frenzied command center abruptly abandoned. Thick stacks of reports, papers, and files covered the detectives’ desks. The air still smelled of lunch, warmed-up cans of Progresso soup and hot dogs from 7-Eleven. Scattered about were household objects with gruesome tales: a HoMedics foot spa bath, suspected of being used to inflict second-degree burns on a 2-year-old.

Nichols approached the desk of her most senior detective, Glen Slade, who was on call that night for after-hours emergencies. Slade, at 53 years old, had been with the squad for 11 years, one of the few detectives with more time there than Nichols. When he joined, he began recording every child abuse case he was assigned in a blue notebook that he kept in his bottom desk drawer. It now numbered more than 2,000.

Slade had watched many detectives in the unit come and go, too disturbed by the cases to stick around for more than a couple years. He felt he had learned to turn it off when he left the office; problem was, sometimes he turned everything else off, too. Those closest to Slade had accused him of being distant, cold. He attended a counseling seminar with his wife to help him cope. He found it so helpful that he started counseling others.

Wearing a golf shirt and reading glasses, Slade leaned back in his chair and slammed down the telephone. “I’ve been working like a dog, but nobody’s been helping me,” he said. “They’ve got all that information up there, and they won’t give it to me over the phone.”

“Well, they’re very upset,” Nichols said. “They’re beside themselves with this kid. All the nursing staff, the doctors, everybody is beside themselves.”

“Then why aren’t they helping me?” Slade asked. He had been trying to gather the basic details of the case, where it happened, the time, the child’s condition. But nurses wouldn’t give information by phone. A fresh legal pad on his desk bore only the child’s name: Joniah Baker.

Slade picked up his leather jacket and followed Nichols outside to meet another detective, Johnsey Vann. The 33-year-old had been home for a half hour when he’d gotten the call to return to work. He left his wife and two young children reading bedtime stories as he collected a change of clothes and a toothbrush. He had to testify in court at 8:15 am, against a father accused of abandoning his 9-month-old beside a trash can. That was less than 12 hours away, and Vann suspected he would be changing clothes in the office bathroom again.

Facing a tight budget year, the police department had cut overtime pay. Instead of receiving a larger paycheck for their after-hours work, detectives would get extra days off. But it was tough to use the time. If the cops didn’t work, the cases didn’t get investigated. For all the time the cops invested, the smaller paychecks were a bruising insult.

Detective Abel Lopez was a father of seven—four biological children and three kids that he and his wife had adopted from Child Protective Services. To make up for the loss of overtime pay, Lopez had picked up two extra security jobs and often didn’t have time to make it home between his double shifts. Instead, he slept in a crowded file room on the third floor of the squad’s office, on a rollaway bed donated by a hotel. He taped a sign to the door that read, “Will shoot first, ask questions later.” On that night, he told Nichols that he would be upstairs and asked her to call him if she needed extra help.

The detectives had grown close, forming their own dysfunctional family with alliances, rivalries, and inside jokes. Most felt isolated from their police brethren, both geographically and emotionally. Instead of working at police headquarters in the Cedars, they worked in the Victorian house, along with CPS, therapists, and a prosecutor, in an atmosphere that was viewed as more welcoming to children. When they gather at parties or bars, cops tell tales, a good-natured competition of one-upmanship, to see who has handled the most outrageous call or who has been the most stupid or brave. But no one wanted to hear the stories of the Child Abuse Squad. Not their colleagues, spouses, friends—not even their own mothers.

Beneath a street light in the parking lot, the detectives gathered around Nichols. She pulled out her iPhone and began to read aloud texts that she had received from a doctor at the hospital:

Blood coming out of his mouth.

Heart keeps stopping.

He’s got subdurals, parietal, occipital, a collapsed right lung.

Healing 8 and 9 ribs, skin injuries old and new.

Blunt force trauma to the chest.

Head likely shaken.

“Eleven months old,” Slade said. All these years, and it still surprised him. They climbed into their cars and headed to Children’s Medical Center.

•••

Hours earlier, around 4 pm, a man and a woman had arrived in the hospital’s emergency room with their son. A triage nurse took the baby from the father’s arms and noticed his skin color, bluish gray. She ran to a critical care room with the baby, shouting, “I need a doctor now!” The urgency in her voice sent every available doctor, nurse, EMT, and medical tech hustling over to help. One doctor stood on a stool and pumped on the baby’s chest; another put a mask over the baby’s face and forced oxygen into his lungs; a respiratory therapist readied equipment for intubation.

Their attempts to establish intravenous access failed. The head physician bored a hole into his bone; they would deliver the fluids there. As they touched the child, they could feel that his body was cold. His temperature registered at 86 degrees.

For the next 40 minutes, the staff continued CPR compressions. They probably wouldn’t have worked so long on an adult. For children, they tended to work longer, harder.

After three hours and 10 minutes, Joniah was still unstable, not moving, not breathing on his own, kept alive by machines. Doctors began an epinephrine drip, hoping to stimulate his heart. Having done all they could, they transferred the child to the nurses in the intensive care unit.

The head ER doctor went to talk to Joniah’s parents. The mother was crying. The father, the doctor thought, appeared stoic, not saying much. She asked the parents what had happened to their son. The parents said he wasn’t acting like himself. Their response raised the doctor’s suspicions, and she asked the hospital’s social worker to call authorities, something she did in about 5 percent of the thousands of cases she handled in the ER every year. Nichols got the call that evening, around 8 pm.